Assembly of phenylaminopyrrolo[1,2-a]pyrazinium salts from N-allenylpyrrole-2-carbaldehydes and phenylhydrazine in the presence of acids

Abstract

The investigation of the reaction of N-allenylpyrrole-2-carbaldehydes with phenylhydrazine demonstrated that, unlike the reactions with hydrazine hydrate, ethyl- and benzylhydrazines, it affords phenylaminopyrrolo[1,2-a]pyrazinium salts as the only products in nearly quantitative yields. The reaction tolerates a wide range of substituted pyrroles, as well as organic and inorganic acids. The synthesized compounds are promising building blocks for the design of pharmaceuticals and their precursors.